To be used 3-5 days before expiration:
"Hello [Name], I hope you are well. I am writing to remind you that your invoice #[Number] for $[Amount] is due on [Date]. If you have already made payment, please ignore this message. If you need additional information or have any questions, I'll be happy to help - thank you for your preference!"

For customers who prefer detailed reminders:
"Hello [Name], your invoice #[Number] for $[Amount] is due on [Date]. For your convenience, you can pay by: [Available payment methods]. If you have already paid or have any questions, please do not hesitate to contact me. Your timeliness is greatly appreciated."

More formal tone for companies:
"Dear, we remind you that the invoice #[Number] for $[Amount] corresponding to [Description of service/product] is due on [Date]. For any questions regarding this invoice or payment methods, please contact [Name of responsible party] at [Phone/Email]. We thank you for your attention."

Friendly tone assuming good faith:
"Hi [Name], I hope you are feeling well. I wanted to contact you because I see that your invoice #[Number] for $[Amount] was due on [Date] and we have not received payment yet. If you have already made the payment, please share the receipt with me. If there are any issues, I would like to know your situation to see how we can help you."

When you need quick confirmation:
"Hello [Name], your invoice #[Number] for $[Amount] was due on [Date], could you please confirm if you have already made the payment? If not, I would like to know when you could regularize your account. I look forward to hearing from you."

For customers normally on a one-time basis:
"Hi [Name], I see that your invoice #[Number] for $[Amount] is [X days] past due, which is unusual considering your excellent payment history. Is there a problem I can help you solve? I'm here to find a solution that works for both of us."

For accounts 15-30 days past due:
"Hi [Name], I have been trying to contact you about your invoice #[Number] for $[Amount] that is [X days] past due. I understand that unforeseen situations can arise and I would like to learn about your current situation to find a solution that works for both of us. We can consider a payment plan or adjust the dates according to your possibilities."

Offering concrete alternatives:
"Hello [Name], your account is $[Amount] past due for [X days]. To help you regularize your situation, I can offer you: 1) Payment plan in [X] installments, 2) Discount of [X]% for immediate payment, 3) Term extension until [Date]. Which option suits you best?"

When there has been no previous response:
"Hello [Name], I am concerned because I have not heard back from you about your invoice #[Number] for $[Amount] that is [X days] past due. I value our business relationship very much and would like to resolve this situation. Please contact me so we can find a solution together."

For arrears of 30-60 days:
"Dear [Name], your account has an overdue balance of $[Amount] corresponding to invoice #[Number] that is [X days] past due. It is important that we regularize this situation to keep your account up to date and avoid affecting your credit history. I offer you the following options: [Specific options]. Please confirm which option is best for you."

When immediate response is needed:
"Dear [Name], your account has a past due balance of $[Amount] that is [X days] past due. To prevent this situation from affecting your credit history and initiating further proceedings, I need your response by [Deadline]. We can still consider payment options that fit your situation."

Formal business tone:
"Dear, your account shows an overdue balance of $[Amount] corresponding to invoice #[Number] with [X days] overdue. In order to maintain the commercial relationship and avoid suspension of services, we request to regularize this situation before [Date]. We remain attentive to your prompt response."

For arrears of more than 60 days:
"Dear [Name], after multiple contact attempts, your account remains $[Amount] past due more than [X days] past due. To prevent this situation from being reported to credit bureaus and legal action, I need you to contact me by [Deadline] to regularize your account."

When consequences need to be specified:
"Dear [Name], your account is $[Amount] past due [X days]. If you do not regularize your situation before [Date], we will proceed to: 1) Report to credit bureaus, 2) Suspension of services, 3) Initiation of legal action. We are still willing to consider a payment agreement."

To document agreements reached:
"Perfect [Name], I confirm our agreement for payment of $[Total Amount] as follows: [Specific Plan Detail]. I will send you friendly reminders prior to each payment date. I appreciate your commitment to regularizing your account."

To confirm payments received:
"Hello [Name], I confirm that we have received your payment of $[Amount] corresponding to invoice #[Number]. Your account is now current. We appreciate your timeliness and look forward to continuing our excellent business relationship."

To remember payment plan installments:
"Hello [Name], I remind you that according to our agreement, the #[Number] installment of $[Amount] is due on [Date]. If you have already made the payment, please share the receipt with me. If you have any inconvenience, please contact me to adjust the plan."