Newbie NEEDS HELP, mandatory-script-verify-flag-failed (Operation not valid with the current stack size) (code 16)

I'm new here and more generally very new in the crypto world, my knowledges are very low, could you please help me to solve my issue please ?

I'm waiting for a refund on my Electrum wallet, it was a 2/3 multisig transaction. I've received, from the third part, a signed transaction.

I've been to coinb.in in the tab "Sign". In first field I entered the private key of my refund address (52 characters begin with "KwS" and ends with "Zig"). In the second big field I entered the signed transaction that was given to me by the third part.

Then I got this message "The above transaction has been signed". But what is strange is that the ouput given by the site is exactly the same than my input.

Then when I try to broadcast transaction, I'm getting following message: "mandatory-script-verify-flag-failed (Operation not valid with the current stack size) (code 16)"

My Raw transaction is: 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

The output address is mine "bc1qmr5cg4pa3lhuwwx0f56w4f3ptvlqv2jnlyl2mf", the output is correct. What's wrong with the non-possible broadcasting ?

What wrong thing did I do please ? As you may have noticed I'm very low-talented about this subject, any help would be great.

Thanks in advance, Dani

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