One of the challenges to the adoption of the decentralised approach to digital ID is a lack of consensus and standardisation of how different stakeholders within the ecosystem can inter-operate. As a means to address this issue, we examine the use of standard application programming interfaces (API) to integrate decentralised digital identification systems to preexisting ones. We first examine the current literature and solutions to (a) assess the attributes necessary to compare and contrast APIs, and (b) create a list of API providers within the decentralised digital ID marketplace, (c) compare the API providers against the attributes established. Based on an API Usability and Adoption framework as our lens, we assessed 19 service providers of APIs against their use cases. We identified that whilst the APIs are maturing, the APIs remain inconsistent and poorly adopted. A clear standard API could assist in better adoption. The guidance provided can inform organisations implementing digital identity and VCs along their adoption journey.