If your receipt footer text looks like the image (1) shown below, then it is most likely that you have uploaded a blank "Thank you" graphic that covers the section shown as (2) "thank you text".

You need to upload a new image that has a height of 50px and is not scaled to be as wide.

Please also review How to setup Receipts and How do I remove the THANK YOU at the foot of the receipt, or change it to something else?