PayPal Integration Issues Resolution

My website has some prevalent issues with PayPal integration that urgently need resolving. The problems lie in payment processing, indicated by the following errors:

• Payment not processing
• Invalid token error
• Missing transaction data

The payment seems to initiate but halts before completion. The website has been built using custom HTML code.

Ideal freelancers for this job should possess:

• Proficiency in HTML coding
• Experience in resolving payment processing issues particularly PayPal
• Ability to swiftly troubleshoot and fix invalid token errors and missing transaction data.

A thorough understanding of PayPal integration is a must for this assignment.