Like @Naktibalda said in the comment: you should split that assertion in two. There are many ways to do it, one is:
$I->seeResponseJsonMatchesJsonPat('$.escrow'); // you need JSON path module; I would expect seeResponseContainsJson could do it, but it appears that it also needs a value...
$I->seeResponseMatchesJsonType(["escrow_status" => "string|null"]);
Another way would be to assert that the response is JSON, convert it to an array and make assertions on that array:
$I->canSeeResponseIsJson();
$data = json_decode($I->grabResponse());
$I->assertArrayHasKey('escrow_status', $data); // might need the assert module
I assumed you used an actor class in your test (hence $I).