The FX Swap template is designed to allow two underlying FX Forward ISINs (based on the same currency pair) to be specified in the generation of an FX Swap ISIN.

In the case of FX swap transactions that are concluded by way of a strategy involving two separate legs, the near leg might be such that would be a spot transaction if it were concluded as a standalone transaction.  However, in the specific context of this approach to an FX swap such a near leg should be regarded as a forward with a spot tenor.

Similarly, if you are looking to generate or retrieve an ISIN for an FX Swap instrument where one of the legs has an spot tenor, it will be necessary to use the ISIN for an FX Forward with the relevant expiry date (being the settlement date for the near leg) for the near leg underlier.