What it means
go.mod lists the modules your program uses. go.sum holds checksums for them. A package was added to your code or to go.mod, but its checksum was not recorded, so the build stops. The build says it in one line: go.sum is incomplete.
How to fix it
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Run
go mod tidyon your machineIt adds the missing entries and removes the ones you no longer use.
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Commit
go.modandgo.sumBoth files must be sent with your code.
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Deploy again
A failed deploy never counts against your plan.
Why it happens
A coding agent adds an import, or edits go.mod by hand, and does not run go mod tidy. The program still builds on a machine whose module cache already holds the package, and fails on a clean server.