I've been having this issue for a few months, after the last upgrade to the store.

Basically if PayPal payment is chosen as the payment method then it takes you to PayPal but with no price entered.

I've checked the form data submitted and ZenCart is setting the price to 0 for a reason I can't work out.

See post data:

HTML Code:
<input type="hidden" name="item_number" value="Store Receipt" />
<input type="hidden" name="upload" value="1" />
<input type="hidden" name="amount" value="0" />
<input type="hidden" name="shipping" value="0.00" />
<input type="hidden" name="tax" value="0.00" />
<input type="hidden" name="tax_cart" value="0.00" />
What I've tried so far:

Reuploading all files to the store except the config files and images
Removing then reinstalling and reconfiguring the PayPal module

I'm out of things to try, can someone please help with this or at least point me in the right direction?