okta-sdk-java: Unable to login to Org - 404 error

I’ve unexpectedly started receiving this exception today, when it was working fine a couple of days ago:

Jan 03 23:21:28 indieauth java[26195]: com.fasterxml.jackson.core.JsonParseException: Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
Jan 03 23:21:28 indieauth java[26195]:  at [Source: (ByteArrayInputStream); line: 1, column: 2]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1851) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:707) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.base.ParserMinimalBase._reportUnexpectedChar(ParserMinimalBase.java:632) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._handleUnexpectedValue(UTF8StreamJsonParser.java:2683) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._nextTokenNotInObject(UTF8StreamJsonParser.java:865) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextToken(UTF8StreamJsonParser.java:757) ~[jackson-core-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.databind.ObjectMapper._initForReading(ObjectMapper.java:4620) ~[jackson-databind-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4469) ~[jackson-databind-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3471) ~[jackson-databind-2.11.0.jar!/:2.11.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.JacksonMapMarshaller.unmarshal(JacksonMapMarshaller.java:86) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultDataStore.getBody(DefaultDataStore.java:474) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultDataStore.execute(DefaultDataStore.java:451) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultDataStore.lambda$getResourceData$1(DefaultDataStore.java:196) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultFilterChain.filter(DefaultFilterChain.java:47) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.cache.WriteCacheFilter.filter(WriteCacheFilter.java:34) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultFilterChain.filter(DefaultFilterChain.java:52) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.cache.ReadCacheFilter.filter(ReadCacheFilter.java:42) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultFilterChain.filter(DefaultFilterChain.java:52) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultDataStore.getResourceData(DefaultDataStore.java:208) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.ds.DefaultDataStore.getResource(DefaultDataStore.java:177) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at com.okta.sdk.impl.client.DefaultClient.getUser(DefaultClient.java:2362) ~[okta-sdk-impl-2.0.0.jar!/:2.0.0]
Jan 03 23:21:28 indieauth java[26195]:         at me.jvt.www.indieauth.authenticators.oktaverify.OktaFacade.triggerVerify(OktaFacade.java:31) ~[classes!/:na]

Code for reference