在英语中，委婉地催款可以采用以下几种方式：

1. Polite Reminder

"I hope this message finds you well. I just wanted to remind you that the invoice for [amount] from [date] is due soon. We appreciate your prompt attention to this matter."

2. Expressing Understanding

"I understand that payments can sometimes take a little longer than expected. Just a gentle reminder that the invoice for your recent purchase, dated [date], is currently due. Your cooperation is greatly appreciated."

3. Suggesting a Follow-Up Date

"I wanted to check in regarding the invoice for your order from [date]. If you haven't had a chance to process it yet, please let me know if you need a little more time. Otherwise, I'll follow up with you next week to ensure everything is on track."

4. Acknowledging Past Business

"We value the partnership we have with your company and always appreciate your timely payments. Just a reminder that the invoice for our recent [service/product], issued on [date], is due. Your prompt payment is always a pleasure to receive."

5. Asking for a Confirmation

"I trust that everything is going well with your current projects. Could you please confirm if the payment for the invoice dated [date] has been processed? We look forward to continuing our successful business relationship."

6. Offering Assistance

"I hope you're doing well. I just wanted to follow up on the invoice for [amount] from [date]. If there are any issues or if you need assistance with the payment process, please don't hesitate to reach out. We're here to help."

7. Using Humor

"I hope you're having a great day! Just a quick reminder that the invoice for [amount] from [date] is due. We're not trying to put any financial pressure on you, but we're also pretty excited about receiving your payment!"

Remember to always maintain a friendly and professional tone, and make sure to provide all necessary information about the invoice, such as the amount due and the date it was issued.