Laravel form data not posting to update controller - php

Question

I am debugging a piece of code one of my team members has submitted, I am not too familiar with Laravel so bear with me if I've missed anything, but basically the form will submit and be redirected to the correct update controller, but when I try to get the result of one of the changed fields in the form, it is just blank.
Index Form Data
<form method="POST" action= "{{ route('apparatus_codes.update' , $apparatusCode->id )}}" class="is-readonly" >
#csrf
#method('PUT')
<tr id="table{{ $apparatusCode->id}}" data-target=".table{{ $apparatusCode->id}}">
<td class="main-bg"> {{ $apparatusCode->id}} </td>
<td class="data main-bg"><input name ="rent" id="rent" value = "{{ $apparatusCode->rent}}"/></td>
<input type="submit" id="save-button" class="save"><img class="mb-1 duration-300 ml-4 inset-0 h-6 w-6" src="/../../img/save-icon.svg" alt="save icon">
</form>
Controller
public function update(ApparatusCodesRequest $request, $id)
{
// find selected apparatus code details
$apparatusCodes = ApparatusCodes::find($id);
$test = $request->input('rent');
echo "TEST".$test;
}
If I echo the $apparatusCodes variable, this will display the correct data from the form on page load. However, I have an input field on the rent field, and the changed value for this field will not come through onto the controller. Also if I echo $request->all or dd($request->all()) there will be no data coming through. I can't tell why nothing is coming through when my form looks to be similar to others I have seen?
There are no errors appearing, it is reaching the intended controller ok it seems, but just not able to retrieve any of the inputted data. Any help would be great. Thanks.
Routes file
Route::post('/apparatus_codes/{id}', [App\Http\Controllers\ApparatusCodesController::class, 'update'] )->name('apparatus_codes.update');
ApparatusCodesRequest.php
<?php
namespace App\Http\Requests;
use Illuminate\Http\Request;
use Illuminate\Foundation\Http\FormRequest;
use App\Models\ApparatusCodes;
class ApparatusCodesRequest extends FormRequest
{
/**
* Determine if the user is authorized to make this request.
*
* #return bool
*/
public function authorize()
{
return true;
}
/**
* Get the validation rules that apply to the request.
*
* #return array
*/
public function rules()
{
// initalising so that memo rule doesn't throw error when creating new apparatus code
$stored_memo = '';
// this is returning id of current apparatusCode
$apparatusCodes_id = $this->route('apparatusCodes');
// this request is used for both create, and update
// we don't want to check for a stored memo when validating a create request
if(!$apparatusCodes_id == null){
// getting the current memo for grantor
// used to check that memo has been updated
$stored_memo = ApparatusCodes::where('id', $apparatusCodes_id)->pluck('memo')->firstOrFail();
}
return [
];
}
public function messages()
{
return [
'memo.not_in' => 'An update to the memo field is required'
];
}
}