Print 0 instead of paypal in invoice

[Ahmar]

Hello,
Please help me about his problem it working fine before (right.jpg).

The problem is that sometimes on a invoice where a customer uses PayPal it is saying "0" in stead of "PayPal". Please see the attached screenshots.

Thanks.

[Ahmar]

Can any one please tell me file name with location which send invoice emails ??
So, I check it.