Unable to install one app into on-prem Exchange 2013 from AppSource

Exchange Server 2013 Enterprise CU21

We are able to install various apps via ECP successfully (Evernote, Salesforce, etc...) into our on-prem Exchange 2013 server, but there is one specific app that when we try to install it we're getting an "ERROR: The app couldn't be downloaded" message. I've tried installing this app via ECP and powershell and both give the same error message. We are able to install this app into a separate Outlook.com address.  The app vendor has not had any suggestions for troubleshooting the issue.  

At this point I don't know if this is an issue with our Exchange server, the appstore, or the app itself.

Logs from an app that will install:

Log Name:      MSExchange Management
Source:        MSExchange CmdletLogs
Date:          5/29/2019 9:28:32 AM
Event ID:      1
Task Category: General
Level:         Information
Keywords:      Classic
User:          N/A
Description:
Cmdlet suceeded. Cmdlet New-App, parameters -MarketplaceServicesUrl "https://o15.officeredir.microsoft.com/r/rlidMktplcWSConfig15" -MarketplaceAssetID "WA104379334" -OrganizationApp "True" -MarketplaceQueryMarket "en-US" -Etoken "" -DownloadOnly "True".

Logs from the app that won't install:

Log Name:      MSExchange Management
Source:        MSExchange CmdletLogs
Date:          5/29/2019 9:29:12 AM
Event ID:      6
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Description:
Cmdlet failed. Cmdlet New-App, parameters -MarketplaceServicesUrl "https://o15.officeredir.microsoft.com/r/rlidMktplcWSConfig15" -MarketplaceAssetID "WA200000041" -OrganizationApp "True" -MarketplaceQueryMarket "en-US" -Etoken "" -DownloadOnly "True".

Any suggestions?  Does this app only work with Office365 & not on-prem exchange?