How can I fix the AI Agent error 'The workflow did not return a response' when calling a Pubmed Research sub-workflow?

Hello Community,

I am setting up an AI Agent to interface with the Pubmed database. I already have a functioning sub-workflow (PubmedResearch) that successfully queries and extracts information for a given number of references on a specific topic. However, when the AI Agent runs, I get the following error and no output. Interestingly, when I run the PubmedResearch workflow manually and copy the input from the AI Agent into the trigger, I receive the expected output (see examples below).

I don’t have a programming background and I’m not sure what else to try. Any ideas on how to resolve this error?

Screenshot errors and outputs:

Error:

JSONCopied
{
  "errorMessage": "There was an error: \"The workflow did not return a response\"",
  "errorDetails": {},
  "n8nDetails": {
    "time": "9.2.2025, 17:14:53",
    "n8nVersion": "1.77.3 (Cloud)",
    "binaryDataMode": "default",
    "cause": {
      "level": "error",
      "tags": {}
    }
  }
}

Output:

JSONCopied
[
  {
    "articles": [
      [
        {
          "PMID": "29183821",
          "citation_count": 135,
          "Abstract": "Total knee arthroplasty (TKA) results in a high degree of patient satisfaction, \n as it provides patients with considerable medium- and long-term benefits in \n terms of quality of life, pain relief and function. Nevertheless, the literature \n reports that up to 30% of patients are dissatisfied. This dissatisfaction is \n directly related to the patients’ quality of life, which they deem insufficient. \n Their quality of life depends on many physical, behavioural, social and \n psychological factors that are not taken into account by functional outcome \n scores. After describing the principles of quality of life evaluation after TKA, \n we will assess the effects of patient-related factors, the surgical technique \n and postoperative program through an exhaustive review of the literature. \n Patient expectations after TKA will then be outlined, particularly return to \n work and return to sports.",
          "Journal": "1. Orthop Traumatol Surg Res. 2018 Feb;104(1S):S41-S46. doi: \n10.1016/j.otsr.2017.04.017. Epub 2017 Nov 26.",
          "Title": "Quality of life after total knee arthroplasty.",
          "Authors": "Canovas F, Dagneaux L."
        },
        ...
      ]
    ]
  }
]

Thanks in advance!