iVend 6.5 Update6 integrated with SAP B1
At the time update Integration Service Configuration service customer was facing below error message


https://www.sap-business-one-tips.com/how-to-solve-failed-to-connect-sld-issue/
https://www.codelessplatforms.com/knowledge-base/knowledge-base/product-tools/specialist-third-party-tools/taskcentre-tools-for-sap-business-one/sap-business-one-connector-tool-error-failed-to-connect-or-logon-to-sld/
One instance from local machine few months ago, we got the similar error message and it was due to changing the SAPB1DB password after installing SAPB1 with its new database.
So suggest you to check with SAP B1 partner .