Error at inserting variables inside html format Mail body

“Hi”+variable+“bye”. It’s a HTML formated mail body. I have a very large code in real. and many variables inside as well. I’ve written the whole code like a first statement in this topic. I’m getting that error end of expression expected. None of the double quotes are misplaced. checked it many times. what else could be the reason.

Kindly check once whether we have used any single quote or brackets along the expression
even we can check that in the input field itself with a red curly line beneath the place where we are missing with a symbol
Cheers @vicky12345678901