- Customer is upgrading from Tridion Sites 9.0 to Tridion Sites 9.5 in Development environment, and is currently using the Bynder ECL provider which is not an addon.
- When deploying their Sites 9.0 ECL extension as an addon to the 9.5 environment, status was "Pending activation".
- The Bynder endpoint has been whitelisted for the Development environment.
- No ECL errors are seen in the Windows event logs or the addon logs of the CM server.

The Bynder plugin listed on below Bynder documentation page is for the pre-addon architecture.  This plugin works for Sites 9.5 when implemented as an ECL provider as was available in earlier product versions.
https://support.bynder.com/hc/en-us/articles/360013872220-Integrate-Bynder-with-SDL-Tridion#UUID-4d2ec59f-909e-6977-65e3-5c8b4d1a2b0d_N1579521912844

It is also possible (and recommended) to wrap the ECL connector as an addon, which facilitates deploying the connector to a Tridion Sites environment.  No packaged download is currently available, but the steps to make the addon are:
- Add all dlls to a zip file and a manifest file.  Example file structure is:
BynderProvider.zip
-- folder BynderProvider
  Bynder dlls and other files
-- manifest.json
- Provide a json configuration file, which is a json-ification of the XML configuration previously done in the ExternalContentLibrary.xml file.  An example of this as below.

{
	"configuration": {
		"BynderProvider": {
			"configuration": {
			    "@xmlns#bynder" : "ecl:BynderProvider",
			    "bynder#EnvironmentUrl" : "https://<YOUR BYNDER ENV>.bynder.com",
			    "bynder#ConsumerKey" : "<CONSUMER KEY>",
			    "bynder#ConsumerSecret" : "CONSUMER SECRET>",
			    "bynder#TokenKey" : "<TOKEN KEY>",
			    "bynder#TokenSecret" : "<TOKEN SECRET>",
			    "bynder#DisplayMetaPropertyFolders" : "enabled",
			    "bynder#HideEmptyMetaPropertyFolders" : "disabled",
			    "bynder#AdditionalMediaPropertiesToShow" : "views,dateCreated",
					"bynder#Derivatives" : "webimage,thul,mini,small,medium,large"
			},
			"namespaces": {
				"bynder": {
					"displayName": "Bynder",
					"stubFolders": ["tcm:2-XX-2"]
				}
			}
		}
	},
	"sitesCm": {
		"isEnabled": true
	}

The addon will have pending status until an editor opens a publication with the ECL mountpoint.  At this point, the connector is deployed.  Note that the TCMID of stub folder should be that of a valid folder item.