Woocommerce Payment Gateways not working

Hello,

I have a strange error with using Paypal/Stripe or any other Payment gateways that is not BACS.

BACS works well and processes the order, however, if any of my customers uses Paypal/Stripe etc, different errors appear.

1) When using stripe, the payment screen refreshes then displays this error on front-end “SyntaxError: Unexpected token < in JSON at position 0”

Console shows this error: “Unable to fix malformed JSON”

However, it still takes their payments, processes it, and places the order on “Processing” with money being captured and authorised.

2) When using paypal, the payment screen refreshes with no error displayed.

Console shows a 502 error with the jquery.js:4 file.

However, the order is placed on hold, waiting on payment.

3) BACS works fine.

Done so far:

1) Cleared all cache
2) Defaulted back to Twenty Seventeen
3) Disabled Plugins one by one
4) Checked Nginx Cache Rules (All fine, never touched since server creation in early 2016)
5) Tried different settings with Stripe and Paypal such as go to their own payment websites etc.
6) Checked for valid SSL Certificate. Still valid.

Please let me know what from here.