Restrict the first name to 20 characters

src/Customer.php

@@ -84,7 +84,7 @@ public function setEmail(string $email): self
      */
     public function setFirstName(string $firstName): self
     {
-        $this->firstName = $firstName;
+        $this->firstName = substr($firstName, 0, 20);
 
         return $this;
     }

tests/CustomerTest.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace ChinLeung\Converge\Tests;
+
+use ChinLeung\Converge\Customer;
+use Illuminate\Support\Arr;
+use Orchestra\Testbench\TestCase;
+
+class CustomerTest extends TestCase
+{
+    /**
+     * The first name of the customer will be truncated to 20 characters.
+     *
+     * @test
+     * @return void
+     */
+    public function the_first_name_will_be_truncated_to_20_characters(): void
+    {
+        $customer = Customer::make()->setFirstName(
+            'Uvuvwevwevwe Onyetenyevwe Ugwemuhwem Osas'
+        );
+
+        $this->assertEquals(
+            'Uvuvwevwevwe Onyeten',
+            Arr::get($customer->toPayload(), 'ssl_first_name')
+        );
+    }
+}