Mihail
may be
Route::group(('/api')
->middleware(AccessCheck::class)
->middleware(FormatDataResponseAsJson::class)
->get('/post',[PostController::class, 'index'])->middleware(FormatDataResponse::class)
->post('/post',[PostController::class, 'add'])->middleware(FormatDataResponse::class)
А если так
Route::group(('/api')
->middleware(AccessCheck::class)
->get('/post',[PostController::class, 'index'])
->middleware(FormatDataResponseAsJson::class)
->post('/post',[PostController::class, 'add'])->middleware(FormatDataResponse::class)