sending "text message" from iPhone to gmail account results in 550-5.7.26 error

using an iPhone 13, from my iCloud account, I just sent a meme to a gmail account holder...a person to whom I've sent hundreds of memes in the past. I received a mailer-daemon message which states: "This is the mail system at host twbgohaavzwvcmta-c-nk-x-00-sms-00.vtext.com.

I'm sorry to have to inform you that your message could not

be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can

delete your own text from the attached returned message.

The mail system (the gmail address and IP address have not been included in this message as I am trying to protect the person's identity and contact information)

said:

550-5.7.26 This mail is unauthenticated, which poses a security risk to the

550-5.7.26 sender and Gmail users, and has been blocked. The sender must

550-5.7.26 authenticate with at least one of SPF or DKIM. For this message,

550-5.7.26 DKIM checks did not pass and SPF check for [mypixmessages.com]

did 550-5.7.26 not pass with ip: [63.55.64.196]. The sender should visit

550-5.7.26 https://support.google.com/mail/answer/81126#authentication for

550 5.7.26 instructions on setting up authentication.

f25-20020a25b099000000b00bf6fcbdfe15si3306368ybj.237 - gsmtp (in reply to

end of DATA command)

I clicked on the "https://support.google.com..." link and the webpage states that: "Starting November 2022, new senders who send email to Google Gmail accounts must set up either SPF or DKIM." It further states: "This requirement doesn't apply to you if you're an existing sender."

I am an existing sender...I've been sending messages to this gmail account holder for years.

My concern is that I'm being required to provide contact or other personally-identifiable information to Google or other third-party vendor...information they have no business having.

What can I do to prevent future occurrences of receiving this 5.7.26 error?

By the way, this error message has occurred on both my iPhone as well as my MacBook Pro.

I look forward to a reply with an offer of assistance at the earliest convenience.

Thanks so much!!