Fix WooCommerce Payments / Checkout error

The checkout page on our woocommerce website throw's an error.
We use WooCommerce Payments.

Example error:
jquery-migrate.min.js?ver=3.3.2:2 JQMIGRATE: Migrate is installed, version 3.3.2
admin-bar-v2.js?ver=11.2-202233:3 Missing data from PHP (wpNotesArgs).
(anoniem) @ admin-bar-v2.js?ver=11.2-202233:3
(anoniem) @ admin-bar-v2.js?ver=11.2-202233:73
contentscript.bundle.js:325 successfully updated user preferred location
?ver=3.0:1 Uncaught (in promise) IntegrationError: In order to create a payment element, you must pass a valid PaymentIntent or SetupIntent client secret when creating the Elements group.

e.g. stripe.elements({clientSecret: "{{CLIENT_SECRET}}"})
at Qn (?ver=3.0:1:221717)
at ur (?ver=3.0:1:228840)
at new n (?ver=3.0:1:233375)
at e.<anonymous> (?ver=3.0:1:237157)
at e.create (?ver=3.0:1:127421)
at upe_checkout.js?ver=4.6.0:1:106715
at f (upe_checkout.js?ver=4.6.0:1:61649)
at Generator._invoke (upe_checkout.js?ver=4.6.0:1:61437)
at Generator.throw (upe_checkout.js?ver=4.6.0:1:62074)
at p (upe_checkout.js?ver=4.6.0:1:82285)
Qn @ ?ver=3.0:1
ur @ ?ver=3.0:1
n @ ?ver=3.0:1
(anoniem) @ ?ver=3.0:1
(anoniem) @ ?ver=3.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
f @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
p @ upe_checkout.js?ver=4.6.0:1
c @ upe_checkout.js?ver=4.6.0:1
Promise.then (asynchroon)
p @ upe_checkout.js?ver=4.6.0:1
a @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
(anoniem) @ upe_checkout.js?ver=4.6.0:1
dispatch @ jquery.min.js?ver=3.6.0:2
v.handle @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
(anoniem) @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
success @ checkout.min.js?ver=6.8.0:1
c @ jquery.min.js?ver=3.6.0:2
fireWith @ jquery.min.js?ver=3.6.0:2
l @ jquery.min.js?ver=3.6.0:2
(anoniem) @ jquery.min.js?ver=3.6.0:2
load (asynchroon)
send @ jquery.min.js?ver=3.6.0:2
ajax @ jquery.min.js?ver=3.6.0:2
s.ajax.s.ajax @ jquery-migrate.min.js?ver=3.3.2:2
update_checkout_action @ checkout.min.js?ver=6.8.0:1
setTimeout (asynchroon)
update_checkout @ checkout.min.js?ver=6.8.0:1
dispatch @ jquery.min.js?ver=3.6.0:2
v.handle @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
(anoniem) @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
init_checkout @ checkout.min.js?ver=6.8.0:1
dispatch @ jquery.min.js?ver=3.6.0:2
v.handle @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
(anoniem) @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
each @ jquery.min.js?ver=3.6.0:2
trigger @ jquery.min.js?ver=3.6.0:2
init @ checkout.min.js?ver=6.8.0:1
(anoniem) @ checkout.min.js?ver=6.8.0:1
e @ jquery.min.js?ver=3.6.0:2
t @ jquery.min.js?ver=3.6.0:2
setTimeout (asynchroon)
(anoniem) @ jquery.min.js?ver=3.6.0:2
c @ jquery.min.js?ver=3.6.0:2
fireWith @ jquery.min.js?ver=3.6.0:2
fire @ jquery.min.js?ver=3.6.0:2
c @ jquery.min.js?ver=3.6.0:2
fireWith @ jquery.min.js?ver=3.6.0:2
ready @ jquery.min.js?ver=3.6.0:2
B @ jquery.min.js?ver=3.6.0:2