Surprise! You can’t append the contents of an Array to another Array in Power Platform Flows.

The input value is of type ‘Array’ which cannot be appended to the variable ‘MatchingContacts’ of type ‘Array’. The action type ‘AppendToArrayVariable’ only supports values of types ‘Float, Integer, String, Boolean, Object’.

Makes sense, but it does demean the supposed simplicity of low-code Flows.

So instead of:

Where value is a collection of results and MatchingContacts is the Array we’re appending to.

You need a more convoluted:

That is, iterate through each result and add each to the Array yourself.