Things to note:
""
makes a literal "
character in a string, so you'll have to double up every one.
- The & is the concatenation operator in a formula, so you can use that to get values outside of your string.
Therefore, this formula should work:
="https://katang.io/?t_pid=1&t_extra={""Source"":"""&A1&""",""Type"":""email"",""Stategy"":""banner""}"
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