Error when proxying requests through a subdomain

My DNS setup is as follows:

CompanyA (Not on cloudflare)
2023.company-a.com -> proxy.company-b.com (CNAME)

CompanyB (Is on cloudflare)
proxy.company-b.com -> IP

When i turn on the cloudflare proxy for proxy.company-b.com i get the following error:

"ERR_SSL_VERSION_OR_CIPHER_MISMATCH"

Our stack is on cloudflare but we have customers who dont want to move their domain to cloudflare. Is there a way to get this to work while having the Cloudflare proxy enabled?

We do have Full (strict) ssl encryption enabled.
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