Fix SPF/ DKIM error (Gmail rejecting our emails)

I've got an issue when sending emails from our domain to G MAiL addresses. The job is to configure SPF/ DKIM so that this issue gets solved. I'm using cloudflare, hosting is cloudways, and domain/ mailserver is hosted at ionos.de

always getting this:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error.

The following address failed:

*******@g mail.com:
SMTP error from remote server for TEXT command, host: gmail-smtp-in.l.g oogle.com (173.194.79.26) reason: 550-5.7.26 This message does not pass authentication checks (SPF and DKIM
both
550-5.7.26 do not pass). SPF check for [*******] does not p
ass
550-5.7.26 with ip: [217.72.192.75].To best protect our users from spam, t
he
550-5.7.26 message has been blocked. Please visit
550-5.7.26 https://support.google.com/mail/answer/81126#authentication fo
r more
550 5.7.26 information. h23-20020a0564020e9700b0049e283e04c9si4086870eda.2
8 - gsmtp


--- The header of the original message is following. ---

Received: from ********([136.244.94.14]) by
mrelayeu.kundenserver.de (mreue109 [213.165.67.113]) with ESMTPSA (Nemesis)
id 1MIMXC-1pTv7o0RBU-00ELGx for <*******>; Tue, 17 Jan 2023
20:45:08 +0100
X-Mailer: Postman SMTP 2.2.2 for WordPress (https://wordpress.org/plugins/post-smtp/)
Content-Type: multipart/mixed;
boundary="=_b3fa3408d3a2890faec61e60902756dd"......
......