Stripe Unexpected token < in JSON at position 0

I am getting this error, it points to client.js line 21. It is the second .then of the fetch(create.php).

The first response returns 200. So, not sure how to fix it. The whole code so far is as extracted from demo instructions. https://stripe.com/docs/payments/integration-builder

See browser console info:

jquery-migrate.min.js?ver=3.3.2:2 JQMIGRATE: Migrate is installed, version 3.3.2
?ver=3.0.0:1 You may test your Stripe.js integration over HTTP. However, live Stripe.js integrations must use HTTPS.
value @ ?ver=3.0.0:1
Ec @ ?ver=3.0.0:1
Sc @ ?ver=3.0.0:1
(anonymous) @ client.js:3
client.js:18 Response {type: "basic", url: "http://amore-paraiso.local/wp-content/plugins/sm-amore-stripe/create.php", redirected: false, status: 200, ok: true, …}body: (...)bodyUsed: trueheaders: Headers {}ok: trueredirected: falsestatus: 200statusText: "OK"type: "basic"url: "http://amore-paraiso.local/wp-content/plugins/sm-amore-stripe/create.php"__proto__: Response
content-tss.js:1 TSS: content-tss.js loaded:  https://js.stripe.com/v3/m-outer-59cdd15d8db95826a41100f00b589171.html#url=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&title=Bride%20%26%20Groom%20%E2%80%93%20Amore%20Paraiso&referrer=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&muid=bb6c8b5b-6e39-4451-91e7-10092d15ec8824d547&sid=3aa75c2f-71f2-493c-ae1b-8f76050ebb800df509&version=6&preview=false
content-ads.js:1 INS: content-ads.js loaded:  https://js.stripe.com/v3/m-outer-59cdd15d8db95826a41100f00b589171.html#url=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&title=Bride%20%26%20Groom%20%E2%80%93%20Amore%20Paraiso&referrer=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&muid=bb6c8b5b-6e39-4451-91e7-10092d15ec8824d547&sid=3aa75c2f-71f2-493c-ae1b-8f76050ebb800df509&version=6&preview=false
VM353:4 hosted page injected
(index):1 Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0
Promise.then (async)
(anonymous) @ client.js:21
content-tss.js:1 TSS: content-tss.js loaded:  https://m.stripe.network/inner.html#url=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&title=Bride%20%26%20Groom%20%E2%80%93%20Amore%20Paraiso&referrer=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&muid=bb6c8b5b-6e39-4451-91e7-10092d15ec8824d547&sid=3aa75c2f-71f2-493c-ae1b-8f76050ebb800df509&version=6&preview=false
content-ads.js:1 INS: content-ads.js loaded:  https://m.stripe.network/inner.html#url=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&title=Bride%20%26%20Groom%20%E2%80%93%20Amore%20Paraiso&referrer=http%3A%2F%2Famore-paraiso.local%2Fexperiences%2Fbride-groom%2F%3F&muid=bb6c8b5b-6e39-4451-91e7-10092d15ec8824d547&sid=3aa75c2f-71f2-493c-ae1b-8f76050ebb800df509&version=6&preview=false

Answer

It turned out the error was on the require './stripe-php/init.php'; on the create.php file.

As I am developing it with WordPress I had it as require plugin_dir_url(__FILE__) . 'stripe-php/init.php';.

Summary:

Make sure the path to require stripe-php/init.php is correct, as below:

require './stripe-php/init.php';

Thanks to @jason who recommended checking the Network tab.