I have used the following script to add a custom customer attribute.

<?php  namespace Harrigo\ContractPricing\Setup;  use Magento\Customer\Setup\CustomerSetupFactory; use Magento\Customer\Model\Customer; use Magento\Eav\Model\Entity\Attribute\Set as AttributeSet; use Magento\Eav\Model\Entity\Attribute\SetFactory as AttributeSetFactory; use Magento\Framework\Setup\InstallDataInterface; use Magento\Framework\Setup\ModuleContextInterface; use Magento\Framework\Setup\ModuleDataSetupInterface;  class InstallData implements InstallDataInterface { protected $  customerSetupFactory; private $  attributeSetFactory;  public function __construct(CustomerSetupFactory $  customerSetupFactory, AttributeSetFactory $  attributeSetFactory) {     $  this->customerSetupFactory = $  customerSetupFactory;     $  this->attributeSetFactory = $  attributeSetFactory; }      public function install(ModuleDataSetupInterface $  setup, ModuleContextInterface $  context) {          $  customerSetup = $  this->customerSetupFactory->create(['setup' => $  setup]);          $  customerEntity = $  customerSetup->getEavConfig()->getEntityType('customer');         $  attributeSetId = $  customerEntity->getDefaultAttributeSetId();          $  attributeSet = $  this->attributeSetFactory->create();         $  attributeGroupId = $  attributeSet->getDefaultGroupId($  attributeSetId);          $  customerSetup->addAttribute(Customer::ENTITY, 'cp_permissions', [             'type' => 'static',             'label' => 'Account Type',             'input' => 'select',             'source' => \Magento\Eav\Model\Entity\Attribute\Source\Table::class,             'required' => false,             'visible' => true,             'user_defined' => false,             'sort_order' => 101,             'position' => 101,             'system' => false,             'adminhtml_only' => true,             'option'         => ['values' => ['Master', 'Branch']]         ]);          $  attribute = $  customerSetup->getEavConfig()->getAttribute(Customer::ENTITY, 'cp_permissions')             ->addData([                 'attribute_set_id' => $  attributeSetId,                 'attribute_group_id' => $  attributeGroupId,                 'used_in_forms' => ['adminhtml_customer'],             ]);          $  attribute->save();          }     } 

The attribute after some difficulty now shows on the form however no longer saved. Initially the attribute didn’t show until i set the source differently and set user_defined to false. I originally changed these in database and all worked however now that i’ve got the installer script almost working (attribute shows and source was set within database) i have noticed that values are not saving.

I have checked and system value is set to 0 / false in customer_eav_attribute table.