How to replace a string with a string containing slash with sed?

Use another character as delimiter in the s command:

printf '%s\n' "$srcText" | sed "s|XPLACEHOLDERX|$connect|"

Or escape the slashes with ksh93's ${var//pattern/replacement} parameter expansion operator (now also supported by zsh, bash, mksh, yash and recent versions of busybox sh).

printf '%s\n' "$srcText" | sed "s/XPLACEHOLDERX/${connect//\//\\/}/"

If your shell supports it:

"${srcText/XPLACEHOLDERX/$connect}"