Full copy of the error message with redacted API Key

rejected 
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headers: {…}
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Authorization: "Bearer [API Key]"
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params: "{\"user\":\"qdr@hypothes.is\",\"uri\":\"https://qdr.syr.edu/atipaper/ideology-of-the-offensive\",\"tags\":[],\"text\":\"<a href=\\\"https://qdr.syr.edu/guidance/ati\\\">\\n<img src=\\\"https://qdr.syr.edu/drupal_data/public/ati_banner_long.png\\\" align=\\\"left\\\"/></a>\\n<br>\\n\\n**Source Excerpt (Source 3):** \\\"Чрезвычайно усложнившаяся вследствие балканских событий международно-политическая обстановка данного времени -- говорилось в постановлении -- требует безотлагательного осуществления некоторых мер по усилению боевой готовности нашей армии.\\\" (136)\\n\\n**Source Excerpt Translation (Source 3):** \\\"'The international political climate of the time,' the resolution said, 'enormously complex as a result of the events in the Balkans, requires immediate implementation of certain measures to enhance the combat readiness of our army.'\\\"\\n\\n**Data Sources:**<br>\\n**Source 1:** https://doi.org/10.5064/F6KW5CXS/3ON1YD <br>\\n**Source 2:** https://doi.org/10.5064/F6KW5CXS/0XYTZG <br>\\n**Source 3:** https://doi.org/10.5064/F6KW5CXS/SM6IT9\\n\\n**Full Citation (Source 1):** A. M. Zaionchkovskii, _Podgotovka Rossii k imperialisticheskoi voine_ (Moscow: Gosvoenizdat, 1926), pp. 297, 306. \\n\\n**Full Citation (Source 2):** A. A. Manikovskii, _Boevoe snabzhenie russkoi armii, 1914-1918_ (Moscow: Vysshii voennyi redaktsionnyi sovet, 1923), vol. III, pp. 7-8.\\n\\n**Full Citation (Source 3):** V. I. Bovykin, _Iz istorii vozniknoveniia pervoi mirovoi voiny: Otnosheniia Rossii i Frantsii v 1912-1914 gg._ (Moscow: Moskovskii Universitet, 1961), p. 136. \\n\",\"target\":[{\"source\":\"https://qdr.syr.edu/atipaper/ideology-of-the-offensive\",\"selector\":[{\"type\":\"FragmentSelector\",\"value\":\"content\",\"conformsTo\":\"https://tools.ietf.org/html/rfc3236\"},{\"type\":\"RangeSelector\",\"endOffset\":636,\"startOffset\":555,\"endContainer\":\"/div[1]/section[1]/div[1]/div[1]/div[1]/div[2]/article[1]/div[1]/div[1]/div[1]/p[31]\",\"startContainer\":\"/div[1]/section[1]/div[1]/div[1]/div[1]/div[2]/article[1]/div[1]/div[1]/div[1]/p[31]\"},{\"end\":27162,\"type\":\"TextPositionSelector\",\"start\":27081},{\"type\":\"TextQuoteSelector\",\"exact\":\"emergency appropriation to start redressing still critical shortages of matériel.\",\"prefix\":\"litary demanded and received an \",\"suffix\":\"49\\nThe development of offensive \"}]}],\"group\":\"2Nopp9mx\",\"permissions\":{\"read\":[\"group:2Nopp9mx\"],\"update\":[\"acct:qdr@hypothes.is\"],\"delete\":[\"acct:qdr@hypothes.is\"]},\"document\":{\"title\":[\"The Ideology of the Offensive: Military Decision Making and the Disasters of 1914 | Qualitative Data Repository\"]}}"
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url: "https://hypothes.is/api/annotations"
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<prototype>: Object { … }
 TypeError: "NetworkError when attempting to fetch resource." hlib.js:132

If not, could the tool display a more user-friendly error message?

Yes, will do.

BTW, the purpose of this prototype is to elicit feedback on what the core capability should ultimately be. I'm all ears!

We'd also be interested to know more about the workflow that motivates all this copying.

We're moving annotations from a private to a public group (and we want both groups to exist, so this isn't about converting the group).

OK, that makes sense. The SciCrunch project does a similar kind of data release.