Automation to lookup Slack Webhook and post message

Brad Close

Hi. I'm trying to create an automation flow that will send a message to a Slack channel that corresponds to the selected value when the user changes the value of a specific field (in this case, it's a custom field).

This was previously implemented with IF/ELSE blocks, but I'm looking to optimise the automation to cut down on automation steps given Atlassian's coming change in automation billing.

I'm trying to use a lookup table where the keys are the possible selectable values for the custom field, and the values are the unique Slack Webhook tokens for different slack channels.

I want the automation to read the updated custom field value, read the Slack webhook token that matches that value, then posts a message to Slack in the channel matching that token.

My flow as it currently stands is:

1. Trigger: Value changes for (custom field)
2. Create Variable: variableName = {{issue.customfield_xxxxx.value}}
3. Create Lookup Table: webhookTable
   1. Key: the potential selectable customfield_xxxxx values
   2. Value: the Slack webhook tokens that correspond to the customfield_xxxxx value selected.
4. Send Slack Message via webhook: the webhook URL is being constructed as "https://hooks.slack.com/services/{{webhookTable.get({{variableName}})

When I trigger this flow, it also reports the same error at the "Send Slack Message via webhook" step:

"Unable to render smart values when executing this flow:Failed to get value for webhookTable.get({{variableName: https://hooks.slack.com/services/{{webhookTable.get({{variableName}})"

(Exact names have been modified for privacy/security).

If it matters, the custom field is a "Select List (single choice)" type.

What am I missing here that is causing this flow to fail?

Subquestion: the webhook tokens do contain "/" characters, so do I have to escape them in some way, and if so, how?

—

Addendum: I changed the Webhook URL to be constructed as:

https://hooks.slack.com/services/{{webhookTable.get(variableName)}}

When I run that, I now get "Error from Slack [301]"

Thanks for any help.

Artyom Karpets _ArtUp Labs_

Hi Brad,

There are two separate problems here.

1. The first error: nested braces. You don't open a second {{ }} inside a smart value, so {{webhookTable.get({{variableName}})}} can't be parsed. {{webhookTable.get(variableName)}} from your addendum is the right form. The / characters in the token need no escaping: the lookup table returns the value as a plain string.

2. The 301: check which URL was actually built. When no key matches, a lookup table returns an empty value and the rule doesn't stop, so the Slack step may be calling a bare https://hooks.slack.com/services/ or a broken path. Add a Log action right before the Slack step:

key=[{{variableName}}]
url=[https://hooks.slack.com/services/{{webhookTable.get(variableName)}}]

Run the rule and open the audit log. The brackets reveal leading or trailing spaces. Typical mismatches:

• Keys match exactly, case and spaces included: Team A and Team A are different keys.
• The table value includes services/ or the whole URL, so that part appears twice.
• The select option was renamed after the table was built.

To rule out the webhook itself, temporarily paste one full webhook URL into the Slack action, with no smart values. If that also returns 301, the webhook is the problem, not the lookup.

A simpler setup: store the full webhook URL as the lookup value and put only {{webhookTable.get(variableName)}} in the URL field. Then the log line shows exactly what Slack receives.

Written with help from an AI assistant.